Anyone who has watched a loved one descend into the fog of dementia knows the tremendous toll that neurodegenerative diseases of aging can exact.

Dementia currently afflicts over 55 million people worldwide; in the US, more than 6 million people — about 1 out of 10 of those 65 years or older — live with dementia. The economic cost of treating and the often uncompensated cost of caring for those sufferers is now more than $600 billion a year. As our population ages, that number will only grow, with one estimate projecting that the number of people with dementia will double by 2060. It is a fate that many of us will one day suffer — according to one recent study, adults over 55 have a nearly one in two chance of eventually developing dementia.

But this week delivered one of the brightest spots in an otherwise dark field. According to a study that followed more than 280,000 people in Wales, older adults who received a vaccine against shingles were 20 percent less likely to develop dementia in the seven years that followed vaccination than those who did not receive the vaccine.

This could be a big deal. There are very few, if any, treatments that can prevent or slow down dementia, beyond good lifestyle habits like getting enough sleep and exercise. The possibility that a known, inexpensive vaccine could offer real protection is enormously meaningful. We have good reason to be confident in the findings: While this study is perhaps the most prominent to show the........

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